Welding apparatus and method for welding tubular skin structures



April 21,1959

L. c. E ET AL 7 2,883,517 WELDING APPARATUS HOD FORWELDING TUBULAR SKINRUCTURE'S Filed Sept. 25, 1957 4 Sheets-Sheet 1 BY MWAED E. fish/DEE I 9f-fe/QVJ Aprll 21, 1959 L. c. RICE ET AL 2,883,517

WELDING APPARATUS AND METHOD FOR WELDING TUBULAR SKIN STRUCTURES FiledSept. 23, 1957 4 Sheets-Sheet 2 L. C. APPARATUS TUB Apnl 21, 1959 RICEETAL 2,883,517

WELDING AND METHOD FOR WELDING ULAR SKIN STRUCTURES Filed Sept. 23, 19574 Sheets-Sheet 3 Q A rrOEA/EVJ' April 21, 1959 L,"(;,' E ETAL 2,883,517

WELDING APPARATUS METHOD FOR WELDING TUBULAR SKIN STRUCTURES 4Sheets-Sheet 4 Filed Sept. 23, 1957 United States Patent WELDINGAPPARATUS AND METHOD FOR WELDING TUBULAR SKIN STRUCTURES Lon C. Rice andBernt 0. Satre, Seattle, and Howard E- Snyder, Mercer Island, Wash.,assignors to Boeing Airplane Company, Seattle, Wash., a corporation ofDelaware Application September 23, 1957, Serial No. 685,541 Claims. (Cl.219-117) Airplane wings and other structural parts, especially when ofthin section, as are those intended for use in high speed aircraft, aresometimes primarily formed as stressed skins with a minimum of internalbracing, each skin consisting of parallel metal tubes contacting andjoined to one another, with a metal skin sheet applied exteriorly atleast, and usually both interiorly and exterior- 1y, to the tubes of theassembly, and joined thereto. An example of such a skin assembly isfound in the co-pending application of Richard S. Reinhold, Serial No.560,399, filed January 20, 1956. Since it is impracticable to buildcomplete wings or the like as single units, the several separate panelsor parts must be joined in a manner to trans mit stresses reliably anduniformly across a joint from one panel to another. A joint structurefor this purpose, disclosed in a Reinhold application Serial No.538,435, filed October 4, 1955 (now Patent No. 2,845,151 issued July 29,195 8) includes finger plates for securement to the tubes at their ends,to which the skin also must be joined.

It will be realized that the joining of the several componentspermanently, reliably, and at sufliciently close intervals, posesproblems which, until solved, may well preclude the adoption of suchskin structures as production parts. Riveting is out of the question,for among other objections it would too greatly weaken the componentspenetrated by numerous rivet holes, and would impose an inordinateweight penalty. Nor are plastic bonding, brazing, or similar procedureswholly suitable, since they are not entirely nor uniformly reliable, noraccessible for inspection to determine their integrity, yet suchprocedures have been attempted, since they have the advantages ofcheapness, lightness, and adaptability to mass production.

Welding is, obviously, the preferred procedure, but the intricacy andsmall size of the components, and their length-the tubes inparticular-make a welding operation by procedures heretofore known adifiicult, costly, and not altogether reliable operation. The assemblyinvolves joining the tubes together along their lines of contact, whilethey are held in the proper contour (usually curved more or less), theapplication of finger plates to the tube ends, and the joining of theskin or skins to the contoured tubes, and to the finger plates, thetubes during this operation being sandwiched between the skins. Weldingrequires each of these operations to be performed independently andusually in the sequence indicated, to which end a conductive member,such as an electrode, must be accurately located within a long tube andpressed hard against its wall, while a complemental electrode is appliedexternally to the assembly, in correct registry with the internal one,or in the operation of joining two parallel tubes along their line ofcontact, both electrodes may have to be inserted within the smalldiameter tubes, to contact and press together the same at just thecorrect spot, but not elsewhere. If such operations can theoretically beperformed, no way had been found heretofore to accomplish the joining ofsuch components of a tube assembly reliably, rapidly, and in a mannersuitable to production operations. To illustrate, a rectangular testpanel three feet by ten z,sss,s17 Patented Apr. 21, 1959 2 feet in area,with no finger plates, was estimated to have some 30,000 weld spots toefiect its assembly. Each such weld spot should be accurately locatedand the weld uniformly accomplished, yet each involves passing a weldingcurrent between the interior and the exterior of a tube, under optimumconditions.

The primary aim of the present invention is to provide a method ofjoining the components of such a tube as sembly, by welding, quickly,reliably, uniformly, and to a degree automatically, in a manner adaptedto varying contours, and regardless of whether the components-beingjoined are tubes-to-tubes, finger plates to tubes, or skins (one orboth) to tubes and finger plates. A further aim is the provision of aconductor or mandrel insertible with in each tube, or a bank thereofinsertible simultaneously within several related tubes, usuallyexpansible and contractible under control, for conducting weldingcurrent between two externally applied electrodes and so joiningintervening interfaces of the components or, if the inserted mandrel isitself an electrode, as it may be if short and readily supported againstthe required pressure, then for conducting welding current passingbetween an externally applied electrode and the inserted one. Stillfurther, it is the aim of this invention to provide welding apparatusadapted to production procedures, according to the method outlinedabove, and in particular, to insure correct location and even spacing ofthe successive welding spots.

The invention is illustrated in simplified and diagrammatic form, forthe accomplishment of the several dilferent assembly procedures outlinedabove.

Figure 1 is an elevational view, looking towards the ends of multipletubes which are being joined simultaneously, to define a planar panel,although a curved panel can be similarly handled. Figure 2 is a similarview, but illustrating the joining of two tubes to define with others asharply curved contour.

Figure 3 is an axial sectional view through two such tubes and themandrels inserted therein, and Figure 4 is a transverse sectional viewof the same.

Figure 5 is a general elevational view of the welding machine, duringthe tube-to-tube joining operation. This illustrates means for spacingthe weld spots uniformly.

Figure 6 is a view similar to Figure l, and Figure 7 is a sideelevational view, both illustrating the operation of joining a fingerplate to a tube.

Figure 8 is a view similar to Figure 1, illustrating the operation ofjoining two skin sheets to the opposite faces of a tube assembly,including finger plates.

Figure 9 is an isometric view of a welding machine of somewhat modifiedform, to adapt it to the welding of a curvedly contoured panel.

Figure 10 is an end elevation, similar to Figure 1 or 8, illustratingmultiple roll welding heads or electrodes, employed in joining skinsheets to a tube assembly or core, such multiple rolls being betteradapted to production operations. Figure 11 is a side elevational viewof the same.

Figure 12 is a view similar to Figure 10, showing the multiple rollelectrodes arranged for welding tubes to tubes, and Figure 13 is a planview, to illustrate a desirable sequence of weld spotting.

Figure 1 illustrates the operation of welding a plurality of tubestogether simultaneously at one of a series of spots that will join thetubes throughout their length. The tubes 9 being thin-walled metal tubesof stainless steel, aluminum alloy, titanium or other suitable metal, itwill be understood that the welding technique employed will be thatwhich is suitable to the particular metal being welded. Assuming thatthe tubes are to be welded into a planar tube assembly, they aresupported upon a suitable table 8, usually of dielectric material,arranged so' that all the tubes are parallel and in contact with one Hrial, and supports'two electrodes 21 and 22, connected to the oppositeterminals of a suitable welding machine. By theapplication of theholddown head the electrodes head 80 notched to fit over the sums arebrought into contact with the two outer tubes of a.

group.

However, it

rent merely through the contacting thin-walled tubes in succession, norcan they be pressed tightly enough to-.

gether at the correct spots, but rather the welding current and pressureshould be concentrated at small spots in the lines ofcontact between thetubes. It is neces sary, therefore, to insert within the tubesconductive elements which will contact each tube and which will serve asa path to carry the current across eachtube from one wall to the otherand so through the walls of the intervening tubes to the conductivemember within the next tube, and so on until the path is completed fromone electrode to the other. These conductive members are in the form ofmandrels (see Figures 3 and 4) of more or less spherical shapedesignated by the numeral 1. They are each supported upon an end of arod 10, and at least at their ends are split, whereby a wedge-likeexpander 11 actuated by a push'pull rod 12 can effect expansion orcontraction of each mandrel from a distant point, as from the exteriorwhen the mandrel is inserted deeply'within its tube. In Figure 3, thecontracted position of the mandrels is shown exagg'eratedly in fulllines, and the expanded position thereof in dash lines.

Referring now to Figure 5, the rods 10 are supported at one end onlyupon a supporting structure 2 which is fixed in position upon a standwith relation to the position of the electrodes 21 and 22. The mandrels1 are so located prior to the beginning of the welding op eration thatthey are in line with the electrodes, and if there are several of them,that they are in a line transversely of the length of the tubes 9. Theyare at an elevation to enter an end of the tubes when the tubes aremoved in the direction of their length. Such movement of the tubes maybe accomplished by supporting them upon a'traveling carriage 81, mountedupon rollers 82 rolling along fixed rails 83. Obviously, the tubes mightbe fixed and the electrodes and mandrels arranged to shift relativethereto, in the direction of the tubes length. The mandrels 1 whencontracted permit the tubes 9 to slide freely past the mandrels, butwhen the mandrels are expanded, they engage the opposite interior wallsof the tubes and urge the tubes closely together at the points nearestthe largest diameter of the mandrel. The electrodes 21, 22 being appliedto the exterior of the tubes at such points of mandrel contact, thewelding current passes through the first tube wall, through the mandreltherein, out at is greatest, and so into the next tube wall and throughits mandrel, and so on to the opposite electrode. The several tubes thuspressed into contact are spot welded to gether, following which themandrels are contracted, relative movement is effected in the directionof the length of the tubes between the mandrels and the tubes, themandrels are again expanded, and again welding current is passed, andthe tubes are again welded together at spots spaced in the direction oftheir length. This process is capable of rapid repetition and a group oftubes can be so welded together in a relatively short time.

The welding machine shown in Figure 5 can accomplish the successiveoperations substantially automatically. The expander rods 12 areconnected to an actu ator lever or the like indicated at 13, which maybe airis not practicable to pass the welding curthe opposite tube wallwhere the pressure or solenoid-operated by the element 14, and a timingelement 15 connected to the element 14 accomplishes reciprocation ofeach expander rod 12 at periodical intervals. A connection at 16 betweenthe timer 15 and a second actuator 17 can be employed to efiectreciprocation of a feed dog 18 engageable with the teeth of aratchet'track 84 which parallels a track 83. The actuation of themandrels also causes advance of the carriage 81 during contraction ofthe mandrels, advancing the tubes 9 thereon by a distance correspondingto the intended spacing between spots.

In Figure 2 the table 8 is replaced by a backing element 8a, also ofdielectric material, and the hold-down head is replaced by a hold-downelement 80m Here the tubes are supported about a sharply curved contoursupport (omitted), and the welding isdesirably accomplished betweenpairs of tubes only. The principle, however, is the same as that alreadydescribed.

The operation described heretofore has been the weld ing of tubes totubes. Similar principles may be em ployed in the other operationsinvolved in the completion of the tube assembly. For example, after thetubes are welded together it is necessary to weld finger plates to thetubes at their ends. Such a finger plate 7 is indicated in Figures 6 and7. Each consists of a plate which is slotted along one edge andcontoured so that its exterior surface lies practically tangent with thetubes to which it is applied. Here, as before, a support or backing head8 is employed, whereon the tubes 9 rest, the backing plate is applied tothe ends of the tubes, prcjecting beyond their ends, as seen in Figure7, and a conductor 23 is inserted within the tube opposite an electrode21a which, in this instance, is provided with a bifurcated contactpoint, each of which engages the finger plate 7 at oppo site'sides ofthe slit therein. The element 23 may itself be an electrode, since thedistance in from the end of l the tube is but short and its supportagainst proper pres sure can beassured, or it too may be an expansibleman trode engaging the exterior of the tube opposite the electrode 21a.Such variations are common in the welding art. The passing of thecurrent and the advance of the electrode may be controlled in anysuitable manner, for instance, in the manner already described.

In like fashion the principles of this invention may be employed in thewelding of skins to tubes. This operation is illustrated in Figure 8where skins 6 and 60 are to be welded simultaneously to the oppositefaces of a tube assembly. Here the mandrel 1a is of slightly differentshape, since it is not intended to nor should it carry current along thelines of contact of one tube with another, for'these lines are alreadywelded together, and it is intended only to carry current from theelectrode 21 to the electrode 22 applied to the opposite exteriorsurfaces'of the assembly, that is, to the skins 6 and 60 opposite theindividual tubes.

Again, the passage of current and the advancement of the assembly toeach new spot location may be effected in the same manner as alreadydescribed. Figure 9 illustrates a machine suitable to efiect such awelding operation. Here the carriage 81 supports a contour former 85 ofa contour conforming to that of the tube assembly and of the skins forapplication thereto. Since the carriage 81 is guided for movement in ahorizontal plane, the contour of the assembly will place the individualtubes at different levels, and in order that the mandrels and theirsupporting rods may enter each such tube, the table may be arranged forelevation or depression by jack means indicated at 86 on its legs. Oneor both of the electrodes also may be vertically adjustable as issuggested at 24.

Heretofore a single pair of electrodes has been suggested. The processis susceptible of performance by multiple electrodes, and it is probablethat such multiple electrodes would be employed for use in production.Figures 10, 11, and 12 illustrate multiple electrodes ap plied to two ofthe operations involved. In Figures and 11, for example, the electrodes21b are in the form of rollers and the companion electrodes 22b are alsoformed as rollers. These roll along the lines of contact between thejoined tubes 9 and the skins 6 and 60 applied thereto. By suitablearrangement of the electrodes or by timing mechanism, not shown, it canbe arranged that a welding current will pass at regular intervalsbetween the electrodes 21!) and 22b and so will be transmitted throughthe passive conductors consisting of the mandrels 1a. It will beunderstood that there is in effect continuous movement in the directionof the length of the tubes between the mandrel and the electrodes 21!)and 22b, all of which are stationary, and the tubes 9 and skins 6 and60. The mandrel will be of a size to prevent deformation of the tubesand yet will not unduly restrict the lengthwise movement of the mandrelwithin the tube.

It has been found in some instances that welding of the tubes togetherwill tend to warp the tube assembly if a number of tubes are weldedtogether simultaneously. It is particularly noticeable that when twotubes are welded together they tend to warp somewhat. It is desirable toprovide for neutralization of this warping effect, and this can be donein a variety of ways. For instance, the tubes may be welded together inpairs while oriented with one side uppermost, after which a similar paircan be reversed, with the side that was uppermost during the welding nowlowermost, and then one such tube of one pair may be welded to anothertube of the other pair, thus neutralizing or reversing the stressingeffect. Another way is suggested in Figures 12 and 13, where theelectrodes 210 at one side of the assembly are each independentelectrodes, as are the electrodes 22c that contact the opposite side ofthe assembly. Arrangements may be made through suitable controls (notshown), but which can readily be accomplished by those skilled in thewelding art, to pass the current between two tubes of a pair and then toskip a pair and to weld a second pair, whereupon the next spot isaccomplished between the skipped tube and the tubes at the oppositefaces thereof. For instance, as suggested in Figure 13, spots a may befirst completed, then spots b, then spots c, then spots d and so, firingthe electrodes in proper sequence.

It will be readily apparent that the present invention is readilyadaptable to any of the operations involving such a tubular assembly,and this regardless of whether the tubes are of round section, ofelongated or elliptical section, or indeed if they be of sinuous or hathalf-section. The invention is applicable wherever it is necessary tolocate a conductor, whether passive or active, in pressure-resistingcontact with the interior wall of a small passageway, in registry with acompanion electrode applied to an exterior wall of the assembly, toeffect passage of a welding current through the assembly and across twoor more contacting surfaces thereof.

I claim as my invention:

1. A method of joining the several tubes of a tube assembly whichincludes parallel contacting tubes which are to be joined together, saidmethod comprising inserting a supporting rod within each of the tubes ofthe assembly, to locate a mandrel of conductive material upon theinserted end of each such rod in a like predetermined locationlengthwise of its tube, disposing the mandrels in contact with the innerwalls of the tubes adjacent their lines of contact with one another, andin alignment with opposite electrodes of a pair, with the several tubesand their inserted mandrels intervening, contacting the two outermosttubes with the respective electrodes, passing a welding current betweenthe electrodes by way of the tubes and the mandrels, effecting relativemovement 6 between the assembly and the electrode and mandrel, in thedirection of the length of the tube, and repeating the contacting andwelding operations, to produce a succession of spot Welds spacedlengthwise of the tubes.

2. A method of joining the parts of an assembly involving parallelcontacting tubes which are to be joined together or to external sheetsspanning such tubes, said method including orienting the assembly withits tubes directed transversely of a pair of cooperating electrodes,entering a supporting rod, hearing at an unsupported end an erpansiblemandrel of conductive material within each tube, with its mandrellocated intermediate the electrodes, expanding said mandrels to contactopposite interior walls of the tubes, contacting the assembly with theelectrodes in the vicinity of each of two separate tubes, and passing awelding current between such electrodes by way of the interposedmandrels, contracting the mandrels, effecting relative movement betweenthe mandrels and the tube assembly in the direction of the tubes length,again expanding the mandrels and repeating the subsequent operations.

3. A method of joining together a plurality of parallel, contactingtubes which are supported in a given contour, said method includingorienting the tubes transversely of a pair of cooperating electrodes,entering a supporting rod, hearing at an unsupported end an expansiblemandrel of conductive material, within each tube of the pluralitythereof, with its mandrel located intermediate the electrodes, expandingall said mandrels to contact the opposite interior walls of the tubes inthe vicinity of their lines of contact, contacting the two exteriortubes in the plurality thereof with the respective electrodes andpassing a welding current therebetween, by way of the expanded mandrelsand the interposed tube walls, contracting the mandrels and effectingrelative movement between the mandrels and the tubes in the direction ofthe tubes length, again expanding the mandrels and repeating thesubsequent operations to produce weld spots at spaced intervals in thelength of the tubes.

4. A method as defined in claim 3, wherein the number of tubes is atleast three, A, B, and C, which comprises initially passing the weldingcurrent between the pair of tubes A and B, next between the pair oftubes B and C, and then alternately between the two pairs.

5. A method as defined in claim 3, wherein the tubes are first weldedtogether in pairs, the pairs being then juxtaposed with alternate pairshaving their original orientation and the intervening pairs reversed topfor bottom, and in the same manner welding together the contacting tubesof adjoining pairs.

6. A method of joining a metal skin upon an assembly of parallel metaltubes joined in contacting relation in a given contour, said methodincluding orienting the tube assembly and the applied skin transverselyof pairs of cooperating electrodes, each pair whereof is disposed inregistry with a different tube, at opposite sides of the surface definedby the assembly, entering a supporting rod, hearing at an unsupportedend a tube-wall-contacting mandrel of conductive material, within eachtube of the assembly, locating the mandrel in line with and intermediatethe corresponding electrodes, and contacting opposite interior walls ofthe tube in the vicinity of such electrodes, contacting the assembly andthe applied skin exteriorly with the electrodes of certain of suchpairs, and passing a welding current therebetween, by Way of themandrels, effecting relative movement between the assembly and skin andthe mandrel in the direction of the tubes length, and repeating thecontacting and welding operations to produce weld spots between the tubeand skin at spaced intervals in the length of the tubes.

7. A method as defined in claim 6, wherein the welding current is passedinitially between each two tubes of dilferent pairs in the assembly,then after relative axial movement between a tube of one such pair and atube of another pair, then again after further axial movement a 7between the initially welded tubes, and so on alternately.

8. A method as defined in claim 6, wherein a plurality of like mandrelsare entered simultaneously within a corresponding number of tubes, andare expanded substantially simultaneously for concurrent passage of thewelding current.

9. A method as defined in claim 6, wherein a skin is to be joinedsimultaneously to both faces of a tube assembly, the method includingthe contacting of the two skins with the respective electrodes, in linewith the expanded mandrel within the interposed tube.

10. A method of joining the components of an assembly involving parallelcontacting tubes and external sheets spanning such tubes, said methodcomprising orienting the assembly with its tube components directedtransversely of a pair of cooperating electrodes, entering a supportingrod, bearing a tube-wall-contacting mandrel of conductive material atits insertedend, within each tube, with the mandrel located intermediatethe electrodes and in contact with the interior tube wall which is to bewelded to another component in the vicinity of the exterior point ofcontact of such other component, contacting the assembly with theelectrodes in the vicinity of each of the two outermostmandrel-receiving tubes, and passing a welding current between suchelectrodes by way of the interposed mandrels, efiecting relativemovement between the mandrels and the assembly in the direction of thetubes length, and repeating the contacting and welding operations. I 1

References Cited in the file of this patent UNITED STATES PATENTS853,241 Helberger May 14, 1907 1,052,753 Rietzel Feb. 11, 1913 1,995,368Sunnen Mar. 26, 1935 Ganahl Oct. 13, 1936

